The invention pertains to the field of electrical fault detection devices connected to AC power lines, and in particular to a fault detection device with lineload miswire protection.
Ground fault circuit interrupters (GFCIs) are well known in the art. Their intent is and always has been to protect the electrical power user from electrocution when hazardous ground fault currents are present. Arc fault circuit interrupters (AFCIs) are a more recent development. Their intent is to interrupt power when either a series arc fault or a parallel arc fault is present in the wiring.
Historical problems with these devices include the possibility of line/load miswiring in the field by an installer, which causes the interrupter device to become inoperable while electrical power is still present, even under hazardous ground fault or arc fault conditions. A variety of methods are used to prevent or attempt to prevent miswiring with varying levels of success. Labels and installation instruction sheets have been used to prevent miswiring, but can be ignored by the installer.
U.S. Pat. No. 5,363,269 discloses revealing reversal of the line and load wires of a receptacle-type GFCI by connecting the test button circuit between load hot and ground.
U.S. Pat. No. 5,541,800 discloses avoiding line/load miswiring by placing a Mylar insulator in one power contact and instructing the user to remove the insulator only after the GFCI trips in response to the t-button.
U.S. Pat. No. 5,600,524 discloses an intelligent GFCI with an audible alarm to alert the user to periodically test the GFCI, circuitry to test the electronics on a periodic basis, and circuitry that determines if the line and load are miswired and that prevents the GFCI from resetting if the miswired condition is identified.
U.S. Pat. No. 5,706,155 discloses an intelligent GFCI with an audible alarm that indicates miswiring.
U.S. Pat. No. 6,040,967 discloses a device that guards against miswiring. Although not fully disclosed in the patent, the device is tripped out when sold. If supply voltage is not connected to the line terminals, (i.e., if the device is line/load miswired), it cannot be reset because the solenoid needs line side power to move a mechanical stop out of the way which otherwise prevents resetting.
There exists a need for a low cost, effective device which prevents line-load miswiring.
Briefly stated, a protection device connected between hot and neutral conductors of an AC power line includes a fault detection circuit which controls a breaker coil operatively associated with a set of interrupting contacts. A capacitance circuit connected between the hot conductor and the neutral conductor stores a charge of a polarity indicative of a line-load miswire. This stored charge independently activates the set of interrupting contacts when the interrupting contacts are closed and the device is miswired, thus preventing the miswired device from providing power.
According to an embodiment of the invention, a protection device connected between hot and neutral conductors of an AC power line includes a fault detection circuit including a first switch controlling a breaker coil operatively associated with a set of interrupting contacts; a capacitance circuit connected between the hot conductor and the neutral conductor; a switching circuit connected to the capacitance circuit and to the first switch; wherein connecting AC power to load terminals of the protection device causes the capacitance circuit to store a first charge of a first polarity indicative of a line-load miswire; and wherein a presence of the first charge causes the switching circuit to activate the first switch and open the set of interrupting contacts when the set of interrupting contacts is closed.
According to an embodiment of the invention, a protection device connected between hot and neutral conductors of an AC power line includes means for detecting a connection of AC supply voltage to improper terminals of the device; means for tripping an interrupting mechanism upon the detection; and means for preventing the protection device from being reset while the AC supply voltage is connected to the improper terminals of the device.
According to an embodiment of the invention, a protection device connected between hot and neutral conductors of an AC power line includes detection means for detecting a fault in the AC power line, the detection means including first switching means for controlling a breaker coil operatively associated with a set of interrupting contacts; capacitance means connected between the hot conductor and the neutral conductor for storing a charge of a polarity indicative of a line-load miswire between the AC power line and the protection device; and second switching means, connected to the capacitance means and to the first switching means, for activating the first switching means when the charge is present in the capacitance means.
According to an embodiment of the invention, a method for preventing a lineload miswire of a protection device connected between hot and neutral conductors of an AC power line includes the steps of storing a charge of a polarity indicative of the line-load miswire between the AC power line and the protection device; and interrupting power within the protection device when the stored charge is present.